The present invention relates to a printing plate element and particularly to a printing plate element capable of forming an image by a computer to plate (CTP) system. The invention also relates to the preparation method of the printing plate element or a printing plate.
An element for CTP which can be easily handled and has a printing ability comparable with that of a PS plate is required accompanied with the digitization of printing data. Recently, many types of CTP by infrared laser recording have been proposed. Among them, a dry CTP including a developing process of the printing machine is noticed, by which a specific developing process is not required. Examples of such the techniques are described in Japanese Patent Publication Open to Public Inspection, hereinafter referred to as JP O.P.I., Nos. 8-507727, 6-186750, 6-199064, 7-314934, 10-58636 and 10-244773.
These are all printing elements each forming an image area or non image area by ablation of the surface layer thereof. Such the printing elements each has problems that the resolving power and the dot quality are low.
Moreover, it is a problem that the contamination of the interior of the exposing apparatus by the scattered matter caused by the ablation of the surface layer. Accordingly, it is often necessary to have a built-in cleaning means such as a specific sucking device or a contamination preventing means such as to cover the surface of the printing plate element by a cover sheet, for solving such the problem. Furthermore, the process cannot be regarded to a complete dry process since it is necessary to remove the ablation residue remained on the plate surface by a means such as wiping or rinsing by an exclusive device.
Besides, a process is called as a wet type CTP in which the solubility to a developer of the image forming layer of the printing plate element is changed by the exposure to light and the image is formed by the development. Such the process has advantages that the anxiety of contamination of interior of the exposing apparatus is little and the high resolving ability can be obtained. However, other problems are caused, such as that an exclusive alkaline developer is necessary to development and the handling ability in a lighted room of the printing plate element is limited since the change in the solubility of the image forming layer is accompanied with a chemical reaction.
The object of the invention is to provide a printing plate element which can be easily handled in a lighted room and is capable of directly forming an image by infrared laser irradiation without an anxiety of contamination of the interior of exposing apparatus, and no specific developing treatment is necessary. Moreover, the object of the invention is to provide a printing plate element having a high resolving power which is protected from a stain caused scratches. Furthermore, the object of the invention is to provide a production method of such the printing plate element and a printing plate.
The object of the invention can be attained by the followings:
1. A printing plate element comprising a substrate and a first component layer, wherein the first component layer contains a first material which is water-insoluble or capable of varying from being water-soluble to being water-insoluble at a prescribed temperature of not less than 60xc2x0 C. and a second material which is water-soluble and has a melting point of 60 to 300xc2x0 C.;
2. The printing plate element described in 1, wherein the second material is a crystalline material;
3. The printing plate element described in 1, wherein the printing plate element comprises a second hydrophilic component layer provided between the substrate and the first component layer;
4. The printing plate element described in 3, wherein the second component layer is a porous layer;
5. The printing plate element described in 3, wherein the second component layer contains a light-heat conversion material;
6. The printing plate element described in 3, wherein the second component layer contains an alkaline colloidal silica and a water soluble polysaccharide;
7. The printing plate element described in 3, wherein the second component layer has a protruding surface structure having a pitch of from 0.1 to 50 xcexcm;
8. The printing plate element described in 3, wherein the printing element comprises a third component layer provided between the substrate and the second component layer, the third component layer containing a light-heat conversion material;
9. The printing plate element described in 1, wherein the first material is a material 1a which is water-insoluble and has a melting point of 60 to 300xc2x0 C.;
10. The printing plate element described in 9, wherein the melting point of the second material is higher than that of the material 1a; 
11. The printing plate element described in 9, wherein the material 1a is in the form of particles, and having an average particle size of 0.01 to 10 xcexcm;
12. The printing plate element described in 9, wherein the material 1a is at least one selected from the group consisting of polyethylene, microcrystalline wax, a fatty acid and a fatty acid ester;
13. The printing plate element described in 1, wherein the first material is a material 1b which is water soluble and capable of coagulating at a temperature of not less than 60xc2x0 C. to form a water-insoluble coagulant;
14. The printing plate element described in 13, wherein the material 1b is at least one selected from the group consisting of a water-soluble protein and a water-soluble glycoprotein;
15. The printing plate element described in 1, wherein the second material has a melting point of 70 to 260xc2x0 C.;
16. The printing plate element described in 1, wherein the second material is an oligosaccharide;
17. The printing plate element described in 16, wherein the oligosaccharide is at least one selected from the group consisting of trehalose, maltose, galactose, sucrose, lactose and raffinose;
18. A method of preparing a printing plate comprising the steps of:
(a) imagewise exposing a printing plate element to laser light and
(b) removing an unexposed area of the printing plate element with an aqueous solution,
wherein printing plate element comprising a substrate and a first component layer, wherein the first component layer contains a first material which is water-insoluble or capable of varying from being water-soluble to being water-insoluble at a prescribed temperature of not less than 60xc2x0 C. and a second material which is water-soluble and has a melting point of 60 to 300xc2x0 C.,
and wherein in step (b), an unexposed area of the first component layer is removed;
19. The method described in 18, wherein step (b) is performed on a printing machine;
20. A printing plate element comprising a substrate having thereon a layer A containing a material 1 which is water-insoluble or capable of varying from being water-soluble to being water-insoluble at a temperature not less than 60xc2x0 C., and a material 2 which is water-soluble and crystalline and has a melting point within the range of from 60xc2x0 to 300xc2x0 C.;
21. The printing plate element described in 20, wherein the printing plate element has a hydrophilic layer B provided between the layer A and the substrate;
22. The printing plate element described in 21, wherein the hydrophilic layer B is a porous layer;
23. The printing plate element described in 21 or 22, wherein the hydrophilic layer B contains a light-heat conversion material;
24. The printing plate element described in any one of 21 to 23, wherein the hydrophilic layer B contains an alkaline colloidal silica and a water-soluble polysaccharide, and having a protruding structure having a pitch of from 0.1 to 50 xcexcm on the surface thereof;
25. The printing plate element described in any one of 21 to 24, wherein the printing plate element has a layer C containing a light-heat conversion material provided between the hydrophilic layer B and the substrate;
26. The printing plate element described in any one of 20 to 25, wherein the material 1 is a material 1a which is water-insoluble and has a melting point within the range of from 60xc2x0 to 300xc2x0 C.;
27. The printing plate element described in 26, wherein the melting point of the material 2 is higher than that of the material 1a; 
28. The printing plate element described in any one of 20 to 25, wherein the material 1 is a material 1b which is capable of being coagulated to form a water-insoluble material at a temperature of not less than 60xc2x0 C.;
29. The printing plate element described in 28, wherein the material 1b is a water-soluble protein or a water-soluble glycoprotein;
30. The printing plate element described in any one of 20 to 29, wherein the material 2 has a melting point within the range of from 70xc2x0 to 260xc2x0 C.;
31. The printing plate element described in any one of 20 to 30, wherein the material 2 is an oligosaccharide;
32. The printing plate element described in 31, wherein the oligosaccharide is selected from the group consisting of trehalose, maltose, galactose, sucrose, lactose and raffinose;
33. A method for preparing a printing plate comprising the steps of
imagewise exposing the printing plate element described in any one of 1 to 13, to laser light, and
removing an unexposed area of the layer A by an aqueous solution;
34. The method for preparing a printing plate described in 33, wherein the step of removing the unexposed area of the layer A by an aqueous solution is performed on a printing machine;
35. A method for preparing a printing plate element comprising the steps of
making a mixture of a powdery material 1b capable of forming a water-insoluble coagulant upon coagulation at a temperature of not less than 60xc2x0 C. and a powdery material 2 having a melting point within the range of from 60xc2x0 to 300xc2x0 C. which is water-soluble and crystalline,
dissolving the mixture into water to make an aqueous coating solution, and
coating the aqueous solution on a substrate and drying;
36. A printing plate element comprising a substrate having thereon a layer A containing at least one of a water-soluble protein and glycoprotein;
37. The printing plate element described in 36, wherein the printing plate element comprises a hydrophilic layer B between the substrate and the layer provided on the substrate;
38. The printing plate element described in 36 or 37, wherein the layer A contains a saccharide or its derivative;
39. The printing plate element described in 37 or 38, wherein the hydrophilic layer B contains a light-heat conversion material;
40. The printing plate element described in 37 or 38, wherein the printing plate element comprises a layer C containing a light-heat conversion material which is provided between the substrate and the layer B;
41. The printing plate element described in any one of 38 to 40, wherein the saccharide contained in the layer A provided on the substrate is an oligosaccharide;
42. The printing plate element described in 41, wherein the oligosaccharide is trehalose;
43. The printing plate element described in any one of 36 to 42, wherein the water-soluble protein contained in the layer A provided on the substrate ovalbumin;
44. The printing plate element described in any one of 36 to 43, wherein the layer provided on the substrate contains a ink adhesion-improving material;
45. The printing plate element described in any one of 36 to 44, wherein the layer A provided on the substrate contains a lubricant;
46. The printing plate element described in any one of 36 to 45, wherein the layer A provided on the substrate contains a matting agent;
47. The printing plate element described in any one of 36 to 46, wherein the hydrophilic layer B is a porous layer;
48. The printing plate element described in any one of 37 to 47, wherein the hydrophilic layer B exhibits alkalinity in the form of a coating solution;
49. The printing plate element described in any one of 37 to 48, wherein the hydrophilic layer B contains at least one selected from the group consisting of a water-soluble protein, a water soluble glycoprotein, a saccharide and its derivative;
50. A method for preparing a printing plate element comprising a substrate having a layer A containing at least one of a water-soluble protein and a water-soluble glycoprotein, the method comprising:
mixing a powder of at least one of the water-soluble protein and glycoprotein with a powdery water-soluble resin to form a powdery mixture,
dissolving the mixture in water to form an aqueous coating solution, and
coating the solution on a substrate and drying to form a layer A;
51. An image forming method comprising:
imagewise exposing a printing plate element comprising a substrate having thereon a layer A containing at least one of a water-soluble protein and a water-soluble glycoprotein to near-infrared laser light to cause all or a part of the exposed layer A to coagulate and
removing an non-coagulated area of the layer A by dissolution with water to form an image;
52. A method for preparing a printing plate comprising:
imagewise exposing a printing plate element comprising a substrate having thereon a layer A containing at least one of a water-soluble protein and a water-soluble glycoprotein to near-infrared laser light to cause all or a part of the exposed layer A to coagulate and
removing an non-coagulated area of the layer A by dissolution with water to prepare a printing plate;
53. An image forming method comprising:
imagewise providing an acid containing ink on the surface of a printing plate element comprising a substrate having thereon a layer A containing at least one of a water-soluble protein and a water-soluble glycoprotein through an ink-jet system to cause all or a part of an ink-provided area of the layer A to coagulate and
removing an non-coagulated area of the layer A by dissolution with water to form an image;
54. The image forming method described in 53, wherein the ink comprises plural inks different in at least one of the kind and the amount of the contained light-heat conversion material, and a difference in the kind of the ink is caused in the extent of coagulation in the ink-provided area of the layer A to enhance gradation;
55. A method for preparing a printing plate comprising:
imagewise providing an acid containing ink on the surface of a printing plate element comprising a substrate having thereon a layer A containing at least one of a water-soluble protein and a water-soluble glycoprotein through an ink-jet system to cause all or a part of an ink-provided area of the layer A to coagulate and
removing an non-coagulated area of the layer A by dissolution with water to prepare a printing plate;
56. The method described in 55, wherein the ink comprises plural inks different in at least one of the kind and the amount of the contained acid, a difference in the kind of the ink is caused in the extent of coagulation in the ink-provided area of the layer A to enhance gradation;
57. An image forming method comprising:
imagewise providing an ink containing a light-heat conversion material on the surface of a printing plate element comprising a substrate having thereon a layer A containing at least one of a water-soluble protein and a water-soluble glycoprotein through an ink-jet system
exposing overall to light having a wavelength within the absorption wavelengths region of the light-heat conversion material to cause all or a part of an ink-provided area of the layer A to coagulate and
removing an non-coagulated area of the layer A by dissolution with water to form an image;
58. The image forming method described in 57, wherein the ink comprises plural inks different in at least one of the kind and the amount of the contained light-heat conversion material, and a difference in the kind of the ink is caused in the extent of coagulation in the ink-provided area of the layer A to enhance gradation;
59. A method for preparing a printing plate comprising:
imagewise providing an ink containing a light-heat conversion material on the surface of a printing plate element comprising a substrate having thereon a layer A containing at least one of a water-soluble protein and a water-soluble glycoprotein through an ink-jet system
exposing overall to light having a wavelength within the absorption wavelengths region of the light-heat conversion material to cause all or a part of an ink-provided area of the layer A to coagulate and
removing an non-coagulated area of the layer A by dissolution with water to form an image;
60. The method described in 59, wherein the ink comprises plural inks different in at least one of the kind and the amount of the contained light-heat conversion material, and a difference in the kind of the ink is caused in the extent of coagulation in the ink-provided area of the layer A to enhance gradation;
61. The image forming method described in any one of 51, 53, 54, 57 and 58, wherein the step of removing the non-coagulated area of the layer A by dissolution with water is performed on a printing machine;
62. The method described in any one of 52, 55, 56, 59 and 60, wherein the step of removing the non-coagulated area of the layer A by dissolution with water is performed on a printing machine;
63. The image forming method described in any one of 51, 53, 54, 57, 58 and 61, wherein the method further comprises a step of drying the ink between steps of providing an ink and removing the non-coagulated area by dissolution with water;
64. The method described in any one of 52, 55, 56, 59, 60 and 62, wherein the method further comprises a step of drying the ink between steps of providing an ink and removing the non-coagulated area by dissolution with water;
65. The image forming method described in any one of 51, 53, 54, 57, 58 and 61, wherein the method further comprises a step of drying the ink between steps of providing an ink and exposing overall;
66. The method described in any one of 52, 55, 56, 59, 60 and 62, wherein the method further comprises a step of drying the ink between steps of providing an ink and exposing overall.
Further preferable embodiments of the invention are described in the followings:
a. The layer A contains both of the materials 1b and 1a. 
b. The material 1a has a shape of granule and the average grain size is within the range of from 0.01 to 10 xcexcm.
c. The averaged grain size of the granule-shaped material 1a is within the range of from 0.1 to 3 xcexcm.
d. The material 1 is selected from the group consisting of a polyethylene, a microcrystalline, a fatty acid ester and a fatty acid.
e. The water-soluble protein is ovalbumin.
f. The alkaline colloidal silica is a necklace-shaped colloidal silica.
g. The alkaline colloidal silica includes a necklace-shaped silica and a spherical silica having an average particle size of from 3 to 20 nm.
h. The water-soluble polysaccharide is a cellulose derivative.
i. The cellulose derivative is a salt of carboxymethyl cellulose.